The present invention relates to digital waveform generating apparatus and, more particularly to a digital waveform generator capable of producing a desired waveshape signal, such as a musical signal waveform, by converting a linearly ascending or descending binary signal for synthesizing a linear piecewise approximation of the desired waveform.
Electronic musical instruments utilizing apparatus for digitally generating a desired musical waveform signal are well known in the art. In one typical embodiment of such a musical instrument, a musical waveform signal is stored in a digital memory in amplitude sampled form and read out of the memory at a selected rate in response to a suitably clocked address counter. The binary waveform signal read from the memory is then converted to an analog form by a digital-to-analog converter and coupled to a speaker system for producing a musical note having a waveshape corresponding to that stored in the memory. U.S. Pat. No. 3,515,792 to Deutsch is exemplary of waveform generation systems of this general type. Although this approach provides considerable flexibility in generating musical waveform signals, in that it permits any waveform to be produced by storing a representation thereof in terms of a succession of spaced amplitude samples, it is also subject to the disadvantage that excessive memory capacity is required to produce a high quality audio signal.
Another prior art technique used to digitally generate musical waveform signals employs a memory storing a set of binary instructions defining successive linear segments of a desired waveform signal. As the binary instructions are sequentially addressed, suitable calculation circuits process the binary instruction for directly generating therefrom a sequence of linear waveform segments representing the desired waveform signal. Co-pending U.S. patent application Ser. No. 88,551 filed Oct. 26, 1979, entitled Complex Waveform Generator For Musical Instrument in the name of Glenn M. Gross and assigned to the assignee of the present application is exemplary of such systems. These systems, which are typically limited to the generation of a single waveform signal at a time, necessitate the use of rather complex and costly calculation circuits especially when generating repetitive waveforms thereby somewhat reducing the utility thereof.
In yet another prior art technique, see, for example, U.S. Pat. No. 4,130,876 to Mitsuhashi, ramp signals are generated and modified through a complex series of multiplications, e.g. squaring operations, to produce a series of curved signal segments which are combined to form a desired musical waveform signal.
It is a basic object of the present invention to provide a musical waveform signal generation system which avoids the disadvantages of the prior art and which is capable of producing a wide variety of musical waveform signals without requiring the use of complex calculation circuits nor excessive memory capacity.